Feb. 12 — Some scientists argue that the evolution of birds from dinosaurs poses a problem of timing. This argument assumes that the current state of knowledge of the fossil record is the literal unalterable truth of the timing of appearances. Archaeopteryx, for example, is in fact older than most of the good specimens of birdlike dinosaurs. Therefore, how could one claim that Archaeopteryx is descended from such creatures? The answer is, in part, that no one is actually making such a claim.

NONE OF THE currently known families of coelurosaurs is considered by paleontologists to be the direct ancestors of birds: Instead, some are interpreted as sharing a more recent common ancestor with birds than with any other known animal, while others are more distantly related to the subgroup containing birds. This is similar to the difference between saying that modern gorillas are the direct ancestor of a position not held by any paleoanthropologist, and saying that gorillas and share a more recent common ancestor with each other than either does with orangutans, gibbons or baboons.

Incidentally, if we were to apply the timing argument used by those opposed to the dinosaur origin of birds to the history of primates, we would conclude that gorillas and chimpanzees are the direct descendants of early humans, since the early human fossil record is better than the early gorilla or chimp record. This is mostly due to the fact that early humans lived and died in environments where fossil bone is more easily preserved, whereas the acidic soils of the rain forests that serve as the home of chimps and gorillas quickly destroy most bones.